1. Field of the Invention
The present invention relates to a head suspension incorporating a piezoelectric actuator that deforms in response to the state of an applied voltage and drives an object according to the deformation. In particular, the present invention relates to a head suspension and a piezoelectric actuator that are reliable and easy to wire.
2. Description of Related Art
Recent information devices are miniaturized and elaborated to necessitate micro-actuators capable of conducting precise positioning. Such precision micro-actuators are particularly needed by optical systems for controlling focal points and inclinations, inkjet printers, and magnetic disk units.
The magnetic disk units are expanding a market and are being expected to improve their performance and storage capacities. Generally, the storage capacity of a magnetic disk unit expands if the storage capacity of a magnetic disk adopted for the magnetic disk unit increases. Increasing the recording density of a magnetic disk without changing the diameter of the disk is achievable by increasing the number of tracks per inch, i.e., by narrowing each track on the disk. To handle such a narrow track, the magnetic disk unit must precisely control the position of a head in a track width direction. Namely, there is a need of an actuator capable of accurately conducting a positioning operation in a very small range.
The magnetic disk unit or a hard disk drive (HDD) includes a magnetic disk and employs a magnetic head to write and read data to and from the magnetic disk. The magnetic head includes a slider that faces a recording surface of the magnetic disk and a transducer incorporated in the slider. When the disk is turned at high speed, the slider slightly floats from the disk to form an air bearing between the disk and the slider.
The magnetic head is supported with a head suspension. The head suspension includes a load beam, a base plate attached to the load beam, and the like. A front end of the load beam supports a flexure made of a thin plate spring. A front end of the flexure holds the slider of the magnetic head.
The hard disk drive must trace the center of a track on the disk at an error of ±10% or lower with respect to the width of the track. Recent high-density disks have a track width of 0.13 μm or narrower to increase the difficulty of tracing the center of the track with the slider. To realize an accurate tracking operation, the disk must be rigid to suppress vibration and the slider must precisely be positioned.
The hard disk drive generally employs a single actuator system that drives a head suspension with a voice coil motor alone. The hard disk drive involves many resonant peaks in a low frequency band. Due to this, it is difficult for the single voice coil motor to drive the slider (head) attached to a front end of the head suspension at high frequencies. Namely, it is difficult for the single actuator system to increase a servo band width.
To cope with this problem, a head suspension employing a dual actuator system has been developed. The dual actuator system employs, in addition to a voice coil motor, a piezoelectric element made of PZT (piezoelectric zirconate titanate) serving as a precision positioning actuator. The piezoelectric element of the dual actuator system minutely drives a front end of the head suspension or the slider in a width direction (sway direction). The dual actuator system usually employs a pair of piezoelectric elements arranged side by side in the width direction, to smoothly drive a driving object, i.e., the slider. The driving object to be driven by the piezoelectric elements of the dual actuator system is light compared with the driving object of the single actuator system, and therefore, the dual actuator system can carry out positioning control at higher frequencies. Unlike the single actuator system, the dual actuator system can maintain a wide servo band width for controlling the position of the slider, to thereby reduce tracking errors.
The applicant of the present invention has proposed in Japanese Unexamined Patent Application Publication No. 2002-050140 a head suspension employing the dual actuator system. This head suspension employs a pair of piezoelectric elements and includes a base plate, a connection plate having a hinge thinner than the base plate, a load beam, and a flexure attached to the load beam. The piezoelectric elements are made of PZT. This head suspension is capable of increasing resonant frequencies. Another head suspension is disclosed in Japanese Unexamined Patent Application Publication No. 2005-312200. This head suspension includes a piezoelectric actuator consisting of a pair of piezoelectric elements. A stationary electrode is arranged on a base of the piezoelectric actuator and is composed of a conductive layer and an interconnecting conductive layer that are formed on an insulating layer. The piezoelectric elements are adhered to the conductive layer. The stationary electrode includes a stainless steel layer, the insulating layer, and the conductive layer.
Each of these related arts arranges a pair of piezoelectric elements for a head suspension. The two piezoelectric elements need four electrodes that need four systems of electrical connection. Namely, each related art must prepare many systems of electrical connection to complicate wiring and deteriorate reliability.